This invention relates to flaw growth monitors or indicators and in particular, but not by way of limitation, to an improved flaw growth correlator for monitoring aircraft flaw growth potential in metal structures.
In U.S. Pat. No. 2,920,480 to Haas and U.S. Pat. No. 3,136,154 to Christensen metal stress monitors are disclosed for attaching to a metal surface. The monitors include metal coupons bonded to the metal surface and having notches, holes, strain gauges, or the like for measuring stress across the area of the coupon so that a correlation may be made between the stress failure of the coupon and potential failure of the metal surface under test.
More recently, U.S. Pat. No. 3,979,949 to Smith discloses a fatigue damage indicator for measuring accumulated fatigue damage on a metal surface. The indicator includes a metal base of uniform thickness with a narrow crack-like slit in the side of the base and having a Teflon parting strip underlying the slit. When the indicator is attached to a metal structure subjected to repeated loading, a correlation may be made between the growth of a crack from the slit and potential fatigue damage incurred in the metal structure.
While the above prior art patents disclose various types of indicators for measuring stress damage using a gauge, coupon, etc., attached to the metal surface under test, none of the indicators provide for accelerated flaw growth in the gauge so that potential flaw growth in a metal surface can be quickly detected and failure of the metal surface may be averted.